Ch 10

There are three main types of muscle tissue:
- Skeletal Muscle Tissue: Primarily under voluntary control. Responsible for movement and stabilization.
- Cardiac Muscle Tissue: Involuntary muscle found only in the heart, responsible for pumping blood.
- Smooth Muscle Tissue: Involuntary muscle found in walls of hollow organs (like intestines and blood vessels).

The primary focus will be on Skeletal Muscle Tissue.
Important to understand the organization of skeletal muscle tissue, how muscle contraction occurs, and how to identify the structures and proteins involved in muscle contraction.

Muscle Fibers: Individual muscle fibers are the basic units that make up muscle tissue.
Each muscle fiber can be grouped into bundles called Fascicles.
- A fascicle comprises a group of muscle fibers, surrounded by connective tissue.
Several fascicles grouped together form the complete Skeletal Muscle.

Endomysium: The connective tissue layer surrounding each individual muscle fiber.
Perimysium: The layer of connective tissue surrounding each fascicle (bundle of muscle fibers).
Epimysium: The outer layer of connective tissue that surrounds the entire muscle.
From deep to superficial:
- Muscle Fiber
- Endomysium
- Fascicle
- Perimysium
- Skeletal Muscle
- Epimysium

Each muscle fiber contains:
- Thin and Thick Filaments: Essential for muscle contraction.
- Thick Filaments: Composed of Myosin proteins. Continuous structure.
- Thin Filaments: Composed of Actin proteins. Discontinuous structure.
Z lines: Structure that reinforces the ends of thin filaments.
Sarcomere: The segment from one Z line to the next, the functional unit of muscle contraction.

Sarcoplasmic Reticulum (SR): Organelle that stores calcium ions needed for muscle contraction.
Terminal Cisternae: The bulging areas of the SR where calcium is specifically stored.
T Tubule: Extensions of the muscle fiber membrane that allow electrical impulses to travel deep into the muscle to trigger contraction.
Triad: Structure formed by one T tubule and two terminal cisternae, essential for muscle contraction signaling.

Signal from the brain travels through the neuron to the muscle fiber.
The electrical impulse travels down the T tubule, reaching the terminal cisternae of the SR, prompting the release of calcium ions.
Calcium binds to Troponin, which causes Tropomyosin to shift and expose binding sites on Actin.
Myosin heads then bind to the exposed actin sites, causing the muscle to contract by pulling actin filaments towards the M line (the center of the sarcomere).

ATP is required for muscle contraction:
- Provides energy for the power stroke of myosin.
- Hydrolysis of ATP leads to contraction; ADP and inorganic phosphate are released during the power stroke.
Muscle relaxation involves ATP as well to detach myosin from actin.

Fast Twitch Fibers: Contract quickly but fatigue quickly.
Slow Twitch Fibers: Contract slowly but are more resistant to fatigue.
Fiber type is influenced by training and genetics; muscle fibers can adapt to training, potentially shifting from one type to another.

Aerobic Metabolism: Requires oxygen, produces about 34-38 ATP per glucose molecule; beneficial for long-duration activities (e.g., marathon running).
Anaerobic Metabolism: Occurs without oxygen, results in only 2 ATP per glucose but allows for quick bursts of energy (e.g., sprinting or weightlifting) and leads to lactic acid accumulation.

This is the connection point between a neuron and a muscle.
Acetylcholine (ACh) is the neurotransmitter that transmits signals from the neuron to the muscle, initiating contraction.

Calcium is critical for muscle contraction by binding to troponin, leading to the exposure of actin binding sites. Low calcium levels can affect both skeletal and cardiac muscle function.